1. Field of the Invention
This invention relates to surgical apparatus, and more particularly, to an improved cryosurgical instrument.
2. Description of the Prior Art
Surgical techniques have been developed for necrosing, adhering and removing or coagulating defective or diseased body tissue by reducing the temperature of the tissue to relatively low values. Various cryosurgical instruments are known for aiding the medical practitioner in this form of treatment. Generally, these instruments include a probe tip which is initially placed in contact with the tissue to be treated and which is then cooled. The cooled probe tip is normally maintained in contact with the treated tissue for a short interval of time. The low temperature required for treatment must be attained rapidly after the probe tip contacts the tissue so that the tissue freezing is localized and the patient is not subjected to prolonged cold treatment. Additionally, it has been found that in certain treatment techniques, the body tissue undesirably adheres to a cooled treatment probe at these low temperatures and it is therefore necessary to provide means for rapidly warming the treatment probe in order to facilitate removal of the probe from the body tissue.
In a known form of cryosurgical instrument, a refrigerant gas under pressure is expanded into a chamber through a flow restriction thus producing a cooling effect commonly known as the Joule-Thomson effect. The probe tip, which is formed by an outer surface of the chamber, is thereby rapidly cooled. The instrument also incorporates means for effecting rapid warming of the probe tip in order to facilitate removal of the probe from the body tissue.
Various arrangements have been employed for cooling and for warming the probe tip. In one arrangement, the flow of a refrigerant gas to the expansion chamber is controlled by a valve located upstream from the chamber. Effluent gas from the chamber is exhausted to atmosphere. Cooling of the probe tip is accomplished by actuating the valve for enabling the flow of refrigerant gas to the expansion chamber and then to atmosphere. Warming of the probe tip is accomplished by interrupting the flow of gas to the expansion chamber and heating the probe tip by electrical means including a coil heater positioned in the probe tip.
In another cryosurgical instrument, probe tip cooling is provided by unseating a flow valve element located downstream of the expansion chamber and simultaneously forming a flow restriction at the chamber inlet by contacting an orifice seat with a moveable conduit. A refrigerant fluid then flows from a source, through the orifice and exhausts through the unseated downstream valve. Warming of the probe tip is accomplished by seating the downstream valve element and simultaneously separating the moveable conduit from the orifice seat thus permitting refrigerant fluid at ambient temperatures to flood the expansion chamber. Upon commencement of the cooling cycle, the instrument is purged of contaminants, such as dirt, ice particles and air bubbles. As the moveable conduit moves towards the orifice seat, refrigerant fluid flows from the source through the orifice momentarily before the conduit is seated on the orifice seat to form the flow restriction necessary to accomplish a Joule-Thomson expansion. This minute amount of unexpanded fluid is used to purge or flush the system of contaminant particles.
However, these arrangements as well as other various cryosurgical instrument arrangements are relatively complex and costly. At times they are relatively difficult for a medical practitioner to handle and do not provide him with the degree of manipulative facility necessary in a medical procedure where the practitioner must devote his close attention to the progress of the procedure. In addition, these known instruments do not provide a sufficient system for purging the instrument of contaminants, which may clog the flow restriction necessary for Joule-Thomson cooling, thereby rendering the instrument inoperative. This is particularly true when ice particles form in the flow restriction due to the rapid expansion of the refrigerant fluid.
In my prior U.S. Pat. No. 3,696,813, issued Oct. 10, 1972 to the same assignee as the present invention, I disclosed an improved cryogenic instrument utilizing the Joule-Thomson expansion principle for cooling the tip of the instrument which is placed in heat exchange relation with an expansion chamber. A quick acting two-way valve independent of and upstream from the expansion chamber is opened during cooling of the tip to exhaust the effluent refrigerating gas to the atmosphere, but upon closing causes interruption of the effluent gas flow to the atmosphere thereby trapping the refrigerant gas in the instrument at ambient temperature since the back pressure prevents further expansion of the incoming gas. This relatively large mass of high pressure gas at ambient temperature rapidly warms the tip thereby rapidly defrosting it.